Magnetron



Feb. 19, 1957 G. R. KILGORE MAGNETRON 2 Sheets-Sheet 1 Filed July 1, 1947 INVENTOR. 620265 R AV/ZGO/GE ATTORNEY Feb. 19, 1957 e. R. KILGORE MAGNETRON 2 Sheets-Sheet 2 Filed July 1, 1947 I v INVENTOR.

Gzaeazi? fyzaaze ATTORN EY Unite States 2,732,342 MAGNETRON George R. Kilgore, Spring Lake, N. L, assignor to Radio Corporation of America, a corporation or Beiaware Application July 1, 1947, Serial N 0. 758,444

15 Claims. (Cl. 31539.57)

.maincathode and the anode for application between the anode and the auxiliary cathode of a voltage whose magnitude may be varied independently of the voltage between the anode and the main cathode which may accordingly remain fixed at a selected optimum magnitude. More specifically, the direct-current voltage difference between the auxiliary cathode and the anode may be so selected or adjusted that a modulating voltage applied between those electrodes will effect frequency or amplitude modulation of the oscillations generated by the magnetron: by such adjustment, either type of modulation may be selected to the substantial exclusion of the other, or both types may concurrently be of substantial magnitude. Preferably, this direct-current voltage is selected to be of magnitude affording frequency-modulation.

Further in accordance with some forms of the invention, the auxiliary cathode and the anode are respectively connected to the conductors of a tuned line, preferably of the coaxial type, whose electrical length is so adjusted or selected with respect to the mean operating frequency of the magnetron that variation of their potential difference effects corresponding variations of the operating frequency but has insubstantial effect upon the amplitude of the oscillations generated by the magnetron.

The invention further resides in features of construction, combination and arrangement hereinafter described and claimed.

.For more detailed understanding of the invention and for illustration of several embodiments thereof, reference is made to the accompanying drawings, in which:

Figure l is a sectional View of a single cavity, multisegment magnetron and a schematic diagram of an associated circuit;

Figure .2 is a plan view, in section, taken on line 22 of Figure 1;

Figure 3 is a sectional view of a multi-cavity magnetron and an associated circuit diagrammatically shown;

Figure 4 is a plan view, in section, taken on line 4--4 .of Figure 3;

Figure 5 is a sectional view of the. main elements of another form of multi-cavity magnetron; and

Figure 6 is a plan view of parts appearing in Figure 5. I Referring to Figures 1 and 2, the magnetron 10 is of the multi-segrnent, singleecavity type having 'a circular array of anode segments or bars 11 disposedwithin, and

about the axis of, the cylindrical resonant anode cavity structure 12. Alternate anode segments 11 are connected 'to'oneend face of'the cavity structure andthe intervening them for generation of high-frequency att 2,72,342 Patented Feb. 19, 1957 ation of the tube. Theend of the cathode 13 is preferably provided with a so-called cathode hat 14, a metal disk of diameter substantially larger than that of thecathode 13 to confine the emitted electrons to that portion of the interaction space immediately surrounding the cathode 13.

For heating the cathode 13 to electron-emissive temperature, there is disposed within the cathode sleeve an electrical heater element 15 connected to a suitable source of alternating or direct current, generically represented by the battery 16. One lead from the source 16 is conneetedrto one end of the hollow inner conductor 17 of a coaxial line 9; the other end of the inner conductor 1'7 is connected by a lead to the cathode 13 which, in effect, serves as a continuation thereof or alternatively the conductor 17 may extend through the tubeenvelope and join or form the cathode 13. The other lead from the source 16 extends through the hollow conductor 17 to that end of the heater 15 which is not connected tothe cathode sleeve 13.

The outer conductor 18 of coaxial line 9 to substantial extent overlaps the metal sleeve 20 which projects through the envelope 8 of the tube from theanodecavity structure 12, thus to form a by-pass condenser effectively coupling the anode to the lower end of the outer conductor of line 9. Preferably, and as shown, a ring 21 of suitable dielectric is interposed between the sleeve 20 and the conductor 18.

The negative terminal of a source of high, direct-current voltage, generically represented by battery 19, is connected to the main cathode 13; the positive terminal of that source is connected to the anode cavity structure 12.

Themagnitude of the anode-cathode voltage is such that high-frequency oscillations are produced within the anode cavity structure in accordance with the usual action of a magnetron, it being understood that there is provided a strong magnetic field parallel to the axis of the interaction space by a magnet, not shown. The output line 9 may be tuned to the operating frequency of the magnetron by adjustment of the tuning plunger 22, and is coupled to the load in any suitable manner, as by the coaxial line 7.

Formodulation of the high-frequency oscillations, there is mounted within the interaction space of the-magnetron an auxiliarythermionic cathode 23 in axial-alignment with :the main cathode 13 and insulated therefrom and from the anode. The auxiliary cathode may also be provided with a hat, not shown, at the end adjacent the main cathode 13. The auxiliary cathode 23 is heated to electron-emissive temperature by a heater element 24 disposed within the cathode sleeve and connected thereto atone end. The heater current is supplied by a suitable alternating or direct current source, generically represented by battery 25. One of the leads from the source 25 is connected to one end of the'inner conductor 26 of a coaxial line 27, the other end of the inner conductor being connected to the auxiliary cathode 23 which therefore serves as a continuation thereof. The other lead from the source 25 extends through'the hollow inner conductor 26 and connects to the other end of the heater element 24.

The upper or open end of the coaxial line 27 to substantial extent overlaps a metal sleeve .29 extending from the anode cavity structure 12 through the envelope 8 of the tube,thus to form a by-pass condenser effectively coupling the anode to the upper end of the line 27 so far as radio-frequency potentials are concerned. Preferably, and as shown, a ring 3% of suitable dielectric material is interposed between the sleeve 29 and conductor 28. The effective electrical length of the line 27 may be varied by adjustment of the tuning plunger 31 to control the magnitude and phasing of the high-frequency potential of the auxiliary cathode with respect to that of the main cathode.

A suitable source of high, direct-current voltage, generically represented by the battery 32, is connected between the anode and the auxiliary cathode 23. By proper adjustment of the magnitude of the voltage between the anode and the auxiliary cathode, the frequency of the oscillations generated by the magnetron may be varied over a substantial range and any attendant undesired change in the amplitude of the output may be minimized by adjustment of the electrical length of the concentric line 27 associated with the auxiliary cathode 23. To elfect variation of the operating frequency in accordance with intelligence to be transmitted, there is effectively introduced in series with the direct current source 32 a source of modulating voltage 33. The operating frequency of the magnetron may thus be caused to deviate from a mean value at, for example, speech or video frequencies and the amplitude of the output, notwithstanding such variation of frequency, remains substantially constant. a

By suitably proportioning the lengths and diameters of the cathodes, the variation in voltage between the auxiliary cathode 23 and the anode required to etfect a given change in frequency may be made substantially greater than that required to etfect the same change in frequency by variation of the voltage between the anode and the main cathode 13: thus, the frequency control attained may be far less critical. Preferably, the main cathode 13 extends along the major portion of the axial length of the interaction space within the anode, and the auxiliary cathode 23 extends along a relatively small portion of this space, as illustrated in the drawings.

With the voltage between the auxiliary cathode and anode so selected or adjusted that with no modulation the electrons from the auxiliary cathode neither supply power to the anode space nor absorb power therefrom, the auxiliary section of the magnetron has only a reactive component of admittance. In such case, the net power output of the auxiliary section is zero and the power output of the magnetron is substantially unchanged in amplitude by the frequency modulation. If, however, the voltage supplied by source 32 is of such magnitude that power is either given up or absorbed by the auxiliary section of the magnetron, there is also amplitude-modulation of the oscillations. When power is given up by the auxiliary section, it is oscillating and has a negative resistance component of admittance: when power is absorbed by the auxiliary section, it has a positive component of admittance. As power absorption may require forced cooling of the auxiliary cathode, this mode of modulation is less desirable. All of the various relative extents of frequency-modulation and amplitude modulation may be obtained without changing the magnitude of voltage 19 or the intensity of the magnetic field threading the interaction space; this permits the optimum modulating conditions to be attained without sacrificing efiiciency of the magnetron as a generator. In general the voltages applied from the sources 19 and 32 are of ditferent magnitude. They may, however, be of the same magnitude provided the main and auxiliary cathodes are of suitably different diameter.

The preceding paragraph applies to all modifications of the invention and is not restricted to that form shown in Figures 1 and 2.

The magnetron 35 shown in Figures 3 and 4, is of the multicavity type having an anode block 36 provided with a pluarlity of cylindrical cavities 37 symmetrically dis- 4 posed about the axis of, and opening into, the central cylindrical interaction space. The anode segments 11A defining the boundary of this space form a circular array of anode elements, all at the same direct-current potential but having different radio-frequency potentials when the tube is oscillating. The main cathode 13 and the auxiliary cathode 23 are in alignment with each other in the axis of the cylindrical interaction space. As in the modification of Figures 1 and 2, the cathodes are insulated from each other and from the anode. The direct-current potential difference between the anode and the main cathode 13, as provided by the source 19, is of magnitude insuring generation of oscillations by at least this section of the magnetron.

For modulation of the oscillations generated by the tube, there is applied between the anode 36 and the auxiliary cathode 23 a voltage from a second source 32 different from the source 19. As in the modification of Figures 1 and 2, the operating frequency, or the mean operating frequency, may be determined by adjustment or selection of the direct current voltage provided by the source 32. For frequency modulating the output of the magnetron, a source of alternating-current signal voltage 33 is elfectively included in series with the directcurrent source 32 between the auxiliary cathode 23 and the anode. As in the modification of Figure 1, any undesired attendant amplitude modulation of the highfrequency output of the magnetron may be minimized by suitably tuning the coaxial line 27 associated with the auxiliary cathode.

In this modification of the invention, the sleeve extension 29A of the anode, which projects externally of the envelope 8A of the tube, exteriorly overlaps the outer conductor 28 of the frequency-control line 27 and the interposed ring 30A of dielectric is accordingly external to the coaxial line 27. In either of these modifications, the coaxial line or lines may be attached to the tube envelope or may be removable therefrom; in the latter case it being understood, of course, that a suitable plug and socket connection is provided for connection of the inner conductor of the respective lines to the corresponding cathode and heater leads.

For coupling of the magnetron to the external load, there may be provided a coaxial output line whose inner conductor 40 extends into one of the anode cavities 37 and is there formed into a loop 41 connected to the outer conductor 42 of the line or to the anode block 36.

In other respects, the construction and mode of operation of magnetron 35 is similar to that of magnetron 10 of Figures 1 and 2.

The magnetron 45 shown in Figures 5 and 6 is of the multi-cavity type comprising an anode block 46 having a plurality of cavity resonators 47 defined by vanes 48 extending radially from a cylindrical interaction space defined by the inner ends of the vanes which accordingly form a circular array of anode segments 11B.

The main cathode 13B and the auxiliary cathode 23B are aligned with respect to each other along the axis of the interaction space. The two cathodes are insulated from each other and from the anode block 46 for application between the anode and the respective cathodes of ditferent operating voltages. The auxiliary and main cathodes are respectively supported by the pole pieces 49 and 50 through which they may extend. The voltage applied by the direct-current source 19 between the anode and the main cathode 13B is of magnitude insuring generation of oscillations by that section of the tube. The voltage applied by the direct current source 32, alone or in combination with the alternating signal or modulation voltage applied from a source 33, may be varied to change the extent to which the electrons from the auxiliary cathode 23B contribute to the oscillations generated by the tube. This section of the tube may as above discussed be oscillating or non-oscillating in dependence upon the selection of the magnitude of voltage 32, but in either event variation of the voltage between the auxiliary cathode and the anode effects modulation of'the output :of the-magnetron independently of the voltage difference between main cathode and anode.

For coupling the magnetron to its load, there may be provided a coaxial line 39A whose inner conductor 40A 7 extends into one of the anode cavities 47 and is there formed into a pickup loop 41A. The lower end of the inner conductor of the line may extend beyond the outer conductor 42A of the line to serve as a probe for exciting a resonant-cavity 'or wave guide. I

From the foregoing examples, it should be evident to those skilled in the art that the invention is not limited thereto and that changesand additions thereto may .be made within the scope of the appended claims.

-What'is claimed is:

1. A magnetron comprising a circular array of anode segments defining a cylindrical interaction space, two cathodes aligned axially of said space :and insulated from each other and from said anode segments, and a tunable coaxial line insulatedfrom said segments and extending from said space with one of said cathodes forming a continuation of its inner conductor.

2. A magnetron of the multi-segmentsingle-cavity type comprising a cavity structure, a circular array of anode segments defining a cylindrical interaction space within said cavity structure, a pair of coaxial lines insulated from each other and coupled to said anode segments and respectively extending from opposite ends of said space, and a pair of cathodes axially aligned in said space and respectively connected to the inner conductors of said coaxial lines.

3. A magnetron of the multi-cavity type comprising a circular array of anode segments defining a cylindrical interaction space, two cathodes aligned axially of said space and insulated from each other and from said anode segments for application of different voltages between the anode segments and the respective cathodes, and a coaxial line having its outer conductor capacitively coupled to the anode segments and its inner conductor connected to one of said cathodes, and means for adjusting the electrical length of said line.

4. A system for generating high frequency energy comprising a magnetron having an anode and two cathodes insulated from each other and said anode, means connected to said anode and one of said cathodes for applying a direct-current difference of potential therebetween for generation of high-frequency oscillations, and means connected to said anode and the other of said cathodes for applying therebetween a difference of potential variable in magnitude to vary the frequency of said oscillations.

5. A system for generating frequency-modulated highfrequency energy comprising a magnetron having an anode and two cathodes insulated from each other and said anode, means connected to said anode and one of said cathodes for applying a direct-current difference of potential therebetween for generation of high-frequency oscillations, and means connected to said anode and the other of said cathodes for applying therebetween a difference of potential having direct-current component greater than said first-named diiference of potential and an alternating-current component which effects variation of the frequency of said oscillations.

6. A system for generating modulated high-frequency energy comprising an anode and two cathodes insulated from each other and said anode, a source of fixed directcurrent voltage connected between said anode and one of said cathodes to effect generation of high-frequency oscillations, a second source of direct-current voltage connected between said anode and the other of said cathodes, means for varying the magnitude of said second voltage at modulation frequencies for modulating the frequency and amplitude of said oscillations, and means for adjusting the average value of said second voltage to vary the relative extents of the frequency-modulation and the amplitude-modulation of said high-frequency oscillations.

7. A system for generating modulated high-frequency energy comprising a magnetron having an anode and two cathodes insulated from each other and said anode, means for applying a direct-current difference of potential between said anode and one of said cathodes for generation of high-frequency oscillations, a coaxial line having its outer conductor capacitively coupled to said anode and its inner conductor connected .to the other of said cathodes, and a source of modulating voltage connected between said anode and said other of the cathodes, and means for adjusting the electrical length of said line to vary the .relative extents of the resulting frequencymodulation and amplitude-modulation of said high-frequency oscillations. i

8. A system for generating frequency-modulated highfrequency energy comprising a magnetron having an anode and two cathodes insulated from each other and said anode, a "coaxial tuned output line having its outer conductor capacitively coupled to said anode and its inner conductor connected to one of said cathodes, a source of direct-current voltage connected between said anode and said one of said cathodes for generation of high-frequency oscillations, a second coaxial line having its outer conductor capacitively coupled to said anode and its inner conductor connected to the other of said cathodes, and a source of modulating voltage connected between said anode and said other of the cathodes for variation of the frequency of said oscillations, and means for adjusting the electrical length of said second coaxial line to minimize amplitude-modulation of said oscillations.

9. A system for generating frequency-modulated highfrequency energy comprising a magnetron having an anode and two cathodes insulated from each other, means connected to said anode and each of said cathodes for applying direct-current voltages between said anode and the respective cathodes, the magnitude one of said voltages resulting in generation of high-frequency oscillations, and a source of modulating voltage connected between said anode and the other one of said cathodes to effect variation of the frequency of said oscillations.

10. A system for generating modulated high-frequency energy comprising a magnetron having an anode and two cathodes insulated from each other, means connected to said anode and each of said cathodes for applying separate direct-current voltages between said anode and the respective cathodes, each of said voltages being of magnitude resulting in generation of high-frequency oscillations, and modulator means for varying one of said voltages correspondingly to modulate said oscillations.

l l. A system for generating modulated high-frequency energy comprising a magnetron having an anode and two cathodes insulated from each other, means connected to said anode and each of said cathodes for applying different direct-current voltages between said anode and the respective cathodes, one only of said voltages being of magnitude resulting in generation of high-frequency oscillations, and modulator means for varying the other of said voltages correspondingly to modulate said oscillations.

12. A magnetron comprising an anode structure defining an interaction space therein, two cathodes positioned in part within said space and insulated from each other and said anode structure, and a tunable coaxial line having its outer conductor coupled to said anode structure and its inner conductor coupled to one of said cathodes.

13. A tunable magnetron comprising a single anode having cavity resonators, and two cathodes insulated from each other and from said anode, said anode functioning as such for both said cathodes, each of said cathodes having means coupled thereto for applying a difference of potential between it and said anode and for applying to the two cathodes potentials differing from each other,

emission from one cathode being adapted to produce high frequency oscillations in the magnetron, and a source of modulation voltage connected to said anode and to said potential applying means of theother cathode for varying the said oscillations over a band of frequencies inclusive of the produced high frequency oscillations.

14. A tunable magnetron comprising a single anode having at least one cavity resonator, and two cathodes insulated from each other and said anode, said anode functioning as such for both of said cathodes, each of said cathodes having means coupled thereto for applying a difference of potential between it and said anode and for applying to the two cathodes potentials difiering from each other, emission from one cathode being adapted to produce high frequency oscillations in the magnetron, and a source of modulation voltage connected to said anode and to said potential applying means of the other cathode for varying the frequency of said oscillations.

15. A tunable magnetron comprising a single anode having at least one cavity resonator, and two cathodes insulated from each other and said anode, said anode functioning as such for both of said cathodes, each of said cathodes having means coupled thereto for apply- '8 ing a difierence of potential between it and said anode and for applying to the two cathodes potentials differing from each other, emission from one cathode being adapted to produce high frequency oscillations in the magnetron, and a source of modulation voltage connected to said anode and to said potential applying means of the other cathode for varying the frequency of said oscillations over a band of frequencies inclusive of the produced high frequency oscillations.

References Cited in the file of this patent UNITED STATES PATENTS 2,144,222 Hollmann Ian. 17, 1939 2,151,766 Hollmann Mar. 28, 1939 2,163,157 Samuel June 20, 1939 2,409,038 Hansell Oct. 8, 1946 2,414,085 Hartman Jan. 14, 1947 2,421,636 McArthur et al. June 3, 1947 2,428,888 Nelson Oct. 14, 1947 2,438,194 Steele et al. Mar. 23, 1948' 2,450,763 McNall Oct. 5, 1948 2,504,739 Shoupp Apr. 18, 1950 2,513,933 Gurewitsch July 4, 1950. 

